The invention relates to a metal honeycomb body or structure, in particular a catalyst carrier body or support for internal combustion engines, with a preferably round, oval or elliptical cross section, including a stack of at least partly structured sheet-metal layers being intertwined in different directions in a jacket tube.
Such honeycomb bodies are known from Published European Application No. 0 245 737, corresponding to U.S. Pat. No. 4,832,998. With structured metal sheets wound or intertwined in opposite directions, a great number of different cross-sectional shapes can be filled out, producing bodies that are highly resistant to alternating thermal strains. The typical somewhat S-shape of the metal sheets is relatively elastic and makes it possible to join all the sheets at their ends to a jacket tube by joining techniques, which has considerable mechanical advantages over spirally wound honeycomb bodies.
However, with catalyst carrier bodies that are exposed to particularly heavy loads and with special shapes, the formation of a durable connection of the metal sheets to a jacket tube can present a problem. In such cases, after a relatively long-term strain, layers of sheet metal may separate in the vicinity of the jacket tube, which can unnecessarily shorten the service life of such a body.
It is accordingly an object of the invention to provide a honeycomb body, in particular with S-shaped, partly reinforced layers of sheet metal, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which has a fastening to the jacket tube that is more resistant to separation.
With the foregoing and other objects in view there is provided, in accordance with the invention, a honeycomb body, especially a catalyst carrier body or structure preferably having a round, oval or elliptical cross section, comprising a jacket tube or tubular sheath, a stack or pile of at least partly structured sheet-metal layers or plates being intertwined in different directions in the jacket tube, the stack having a given length dimension and a given width dimension, and at least one of the sheet-metal layers having a greater thickness over at least part of at least one of the given dimensions than others of the layers, the at least one sheet-metal layer having a greater thickness being formed of thicker sheet metal than the others of the layers or being formed of a plurality of identically structured thinner metal sheets resting closely against one another.
In accordance with another feature of the invention, the stack has a middle, and the at least one sheet-metal layer having a greater thickness than the others of the layers includes one of the sheet-metal layers disposed approximately at the middle of the stack. This presents no problems in terms of production techniques, in particular because the greater thickness is attained by stacking together a great number of thin metal sheets. The reinforcement of the middle layer of sheet metal leads to a symmetrical structure of the resulting body, which is also advantageous in terms of force distribution.
In accordance with a further feature of the invention, the stack has an upper outer layer and a lower outer layer, and the at least one sheet-metal layer having a greater thickness than the others of the layers includes at least one of the outer layers. The use of thicker uppermost and lowermost sheet-metal layers in the stack, optionally in combination with a thicker middle layer, again leads to a very symmetrical structure of the resulting body. Since the uppermost and lowermost sheet-metal layers of the stack are additionally folded together while being wound in opposite directions, this alternative has the advantage of permitting a correspondingly thinner sheet-metal layer or a correspondingly lower number of metal sheets to be used, in order to attain the same thickness of the resulting ribs as when only the middle layer is thicker.
Therefore, the stack or pile of metal sheets has individual layers of greater thickness on its top and/or bottom and/or in its interior, either because thicker metal sheets are used, or because in this layer a plurality of identically structured thin metal sheets rest closely against one another.
In accordance with an added feature of the invention, the jacket tube has an oval or approximately elliptical shape giving the honeycomb body slightly rounded or slightly rounded and straight regions, and the at least one sheet-metal layer having a greater thickness than the others of the layers forms at least one approximately S-shaped connecting bridge between the regions, the at least one bridge jointly conducting forces acting on the outside of the honeycomb body into the interior thereof. Oval or elliptical shapes provide particular advantages. Since oval or elliptical shapes are vulnerable to deformation if the internal pressure varies, an approximately S-shaped connecting bridge between the straight or slightly rounded regions of the jacket tube is a structure that is particularly advantageous for the stability of this shape. Once again, the forces arising on the outside in the vicinity of the jacket tube are distributed substantially more uniformly into the interior of the catalyst carrier body by individual thicker layers, and among other advantages this also reduces the noise being generated.
In accordance with an additional feature of the invention, the at least one sheet-metal layer having a greater thickness than the others of the layers is in the form of smooth sheet-metal layers. While many different sheet-metal structures are known in the prior art for forming channels through which exhaust gas can pass, the most frequently used kind of structure is nevertheless an alternating layering of smooth and corrugated sheet-metal layers. In this case, it is suitable to reinforce some of the smooth sheet-metal layers. Smooth sheet-metal layers deform less under tensile strain than corrugated ones and can therefore transmit the resultant forces better than corrugated sheet-metal layers.
In accordance with yet another feature of the invention, the stack has an axial length as seen in axial direction of the honeycomb body, and the at least one sheet-metal layer having a greater thickness than the others of the layers does not extend over the entire width of the stack or in other words over the entire axial length of the honeycomb body but rather is discontinuous and includes at least one strip oriented in the axial direction. When the at least one strip is a plurality of strips, they are disposed in succession in the axial direction.
Therefore, the thicker layers may also include two or more individual strips, instead of filling the entire width of the stack, or in other words the entire axial depth of the resultant honeycomb body. The effect of these thicker layers of metal sheets is that because of their greater mechanical strength, they cannot be easily separated from the jacket tube. Moreover, these thicker layers can also firmly hold the layers of sheet metal adjoining them jointly, so that either these layers do not separate from the jacket tube, or at least they are firmly held by the thick layer despite separating.
In particular, it is advantageous for such strips to be inserted only on one or both end surfaces. On one hand, this economizes on material, but on the other hand it is suitable in terms of the various fastening possibilities and conventional brazing methods for catalyst carrier bodies, for example. With catalyst carrier bodies that are brazed only on the end surface, for instance, the desired success can be attained by providing sheet-metal layers that are thicker only on the end surface. Therefore, in accordance with yet a further feature of the invention, the stack has end surfaces, and the at least one strip has a width of substantially from 1 to 3 cm in the axial direction and is disposed at least at one of the end surfaces.
In principle, however, other arbitrary positions of the thicker sheet-metal layers within the catalyst carrier body are also possible, with the locations particularly depending on the size of the brazed zones between the jacket tube and the sheet-metal layers.
In accordance with a concomitant feature of the invention, the stack has end surfaces, the jacket tube and the stack are at least partly high-temperature brazed at least at one of the end surfaces, and the high-temperature brazing extends to a depth of substantially from 3 to 10 millimeters. High-temperature brazing that extends preferably to a depth of several millimeters is used on the end surface for specialized honeycomb bodies as well. If the individual layers of sheet metal in the stack are brazed to one another, preferably at one or both end surfaces, then the thicker layers conduct the tensile forces arising in the outer region in the vicinity of the jacket tube into the interior of the honeycomb body, so that the forces are distributed over substantially more connecting points, thereby considerably prolonging the service life of the body.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a honeycomb body, in particular with S-shaped, partly reinforced layers of sheet metal, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims, and also expressly applies to any cross-sectional shapes that can be filled with a stack of metal sheets wound in opposite directions.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.